Prediction of Urban GNSS Availability and Signal Degradation Using Virtual Reality City Models

Joe Bradbury

Abstract:	A software toolkit has been developed by UCL/Spirent Communications that can harvest geometric data from computerised models of urban environments. This data can then be used to predict satellite availability and receiver position error due to multipath. Generally, methods that exist to predict satellite availability use line of sight (LOS) propagation models only. This paper identifies reasons as to why the LOS only approach is inappropriate. A simulator has been developed to predict satellite availability via a range of sophisticated propagation modes, including diffraction and reflection. This simulator has been designed and written such that it will ultimately be used by low resource devices. An overview of the simulator and the simulation process is first provided. The definition of an available signal is then discussed. Description is given of a model developed to determine the signals arriving at an antenna via diffracted propagation. Further to this, description is given of a separate propagation model that assesses the level of signal obstruction within a theoretical volume known as a Fresnel zone. It is within this zone that the majority of the energy for transmission between transmitter (GNSS satellite) and receiver is contained. The third signal propagation model provides an estimate of signals that are received by reflected paths. A demonstration of how this tool can be used is provided, and simulation results are shown. These simulated results are then compared with real-world observations in order to test and validate the three signal propagation models. A discussion of the results is provided before conclusions and details of continuing work are given.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	2696 - 2706
Cite this article:	Bradbury, Joe, "Prediction of Urban GNSS Availability and Signal Degradation Using Virtual Reality City Models," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 2696-2706.
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